For the management of labor pain, the ideal programmed intermittent epidural bolus (PIEB) amount for 0.1% Ropivacaine and 0.5 µg/mL Sufentanil was 9 mL, whereas, for 0.075% Ropivacaine and 0.5 µg/mL Sufentanil, it was 10 mL, with a forty-minutes interval, according to a biased coin up-and-down sequential allocation trial.

By using the biased coin design-up-and-down method (BCD-UDM), Xin Ran et al. sought to determine the effective analgesia of Ropivacaine concentrations of 0.075% and 0.1% in combination with 0.5 g/mL Sufentanil in 90% of females (EV90) and determine whether there is a variation in EV90 with elevating Ropivacaine concentration.

Overall, 103 primiparous females (gestational age between 37 and 42 weeks) were divided into 2 groups, group A (n = 52) and group B (n = 51). The treatment for parturients in group A was 0.5 µg/mL Sufentanil and 0.075% Ropivacaine, whereas the treatment for parturients in group B was 0.5 µg/mL Sufentanil and 0.1% Ropivacaine. EV90 was calculated using biased coin up-and-down sequential allocation methodology.

The degree of sensory block, motor block, and side effects (pruritus, urinary retention, and hypotension) were the secondary endpoints ascertained. According to the isotonic regression approach, group A's EV90 was 10 mL while group B's EV90 was 9 mL. Lowest level of sensory block was noted to be T12 and the greatest was T8. Additionally, the volume of PIEB dropped as Ropivacaine's concentration increased. Only 4 parturients reported complaining of motor block, and there were no cases of hypotension noted.